diff --git a/changelog.d/11677.bugfix b/changelog.d/11677.bugfix
new file mode 100644
index 000000000000..5691064a303c
--- /dev/null
+++ b/changelog.d/11677.bugfix
@@ -0,0 +1 @@
+Fix wrong variable reference in `SimpleHttpClient.get_json` that results in the absence of the `Accept` header in the request.
diff --git a/synapse/http/client.py b/synapse/http/client.py
index fbbeceabeb6a..ca33b45cb21f 100644
--- a/synapse/http/client.py
+++ b/synapse/http/client.py
@@ -588,7 +588,7 @@ async def get_json(
         if headers:
             actual_headers.update(headers)  # type: ignore
 
-        body = await self.get_raw(uri, args, headers=headers)
+        body = await self.get_raw(uri, args, headers=actual_headers)
         return json_decoder.decode(body.decode("utf-8"))
 
     async def put_json(